Severe Thunderstorm Warning 18, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
1140AM MDT Sat Jul 1 2023

.SYNOPSIS...

Breezy and gusty west winds are expected today over the plains
and valleys of Central and North Central Montana, with the
strongest winds expected along the Rocky Mountain Front. High
temperatures will peak in the 80s to mid-90s across the Northern
Rockies, with widely scattered to numerous showers and
thunderstorms possible this afternoon and early evening south of
the Montana Hwy 200 corridor. A cold front will drop south across
the Northern Rockies on Sunday, cooling some location by 5 to 15
degrees.

&&

.UPDATE...

Inherited forecast is performing nicely; therefore, no updates are
made, at this time.
- Fogleman

&&

.DISCUSSION...

Today through Sunday...Fast, zonal flow aloft over the Northern
Rockies through tonight will help to maintain above to well above
normal temperatures, breezy and gusty west winds, and low relative
humidity values across the Northern Rockies. While high wind
criteria wind speeds and gusts are not currently expected through
this evening, NBM probabilistic data does supports a 70% or greater
chance of seeing wind gusts in excess 41kts across portions of the
East Glacier Park Region, Southern Rocky Mountain Front, Northern
and Southern High Plains, and Eastern Glacier/Western Toole/Central
Pondera Counties. High temperatures will climb an additional 2-5
degrees (from Friday) across Southwest through North Central Montana
thanks to these breezy and gusty west winds, with most locations
peaking in the 80s to mid-90s. Hottest temperatures today are
expected over the plains of Central and North Central Montana east
of the I-15 corridor. While widely scattered to numerous showers and
thunderstorms are possible this afternoon and early evening south of
the Montana Hwy 200 corridor, areas north of this corridor will
remain dry through tonight. A cold front will then begin to advance
south and across the Northern Rockies during the day on Sunday,
switching surface winds to the north and cooling some locations
across Central and North Central by 5 to 15 degrees.

Monday through Tuesday (Independence Day)...cluster analysis on
Monday supports and amplified longwave ridge over the Eastern
Pacific points north to over the Northwest Territories in Canada,
with a positively tilted longwave trough orientated from over
Central Canada points southwest into portions of the Pacific
Northwest and Northern Rockies. By Tuesday, the longwave ridge over
the Eastern Pacific slides slightly eastward to near the western
seaboards of the CONUS, with northwest flow remaining in place over
the Northern Rockies as the positively tilted longwave trough begins
to lift northeast to near Hudson Bay. An embedded shortwave dropping
southeast within the downstream side of the ridge axis from Monday
night and through the day on Tuesday will move over the Northern
Rockies as the main longwave trough axis slides east of the region,
providing support for widespread precipitation across the Northern
Rockies over the timeframe, especially to Central Montana. Numerous
reinforcing cold fronts on Monday and Tuesday will usher in
progressively cooler/below normal temperatures, with high
temperatures on Tuesday being well below normal and in the upper 50s
to near 70 degrees across Southwest trough North Central Montana.
Snow levels late Monday night and into the day on Tuesday could fall
to as low as 8000 feet across Central Montana, which could lead to
some minor snow accumulations across the higher peaks.

Wednesday through next Saturday...high temperatures slowly begin to
moderate closer to normal as the upper level ridge over the Eastern
Pacific attempts to build east to over the Northern Rockies,
remaining just to the west over the Pacific Northwest and placing
the Northern Rockies beneath unsettled northwest flow aloft. This
unsettled northwest flow aloft pattern will provide for daily
chances for isolated to scattered showers and storms across
Southwest through North Central Montana, with the best coverage of
showers and storms being over the higher terrain. - Moldan

&&

.AVIATION...
1140 AM MDT Sat Jul 01 2023 (01/18Z TAF Period)

Increasing winds aloft will result in gusty surface winds across the
area today, especially at KBZN, KGTF, KHLN, KCTB, and KHVR. While
winds will result in some areas of mountain wave turbulence, expect
VFR conditions to prevail. Main concern this afternoon will be some
TSRA activity across SW MT. While most of this should be isolated
pop up SHRA/TSRA, a more organized complex of storms is on track to
reach KHLN around 1820z, and will bring a period of gusty winds and
rain to the terminal. Ludwig

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  91  57  84  48 /  10   0   0   0
CTB  89  55  78  43 /   0   0  10  10
HLN  90  55  89  52 /  20   0   0   0
BZN  85  50  87  49 /  40  30  10  10
WYS  75  40  77  39 /  60  70  20  20
DLN  82  48  85  46 /  40  20  10  10
HVR  96  59  81  48 /   0   0  10  30
LWT  84  54  81  47 /  10  10  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

http://www.weather.gov/greatfalls

Special Weather Statement
National Weather Service Great Falls MT
1204 PM MDT Sat Jul 1 2023

MTZ301>303-307-308-012115-
East Glacier Park Region-Northern High Plains-
Eastern Glacier, Western Toole, and Central Pondera-
Southern Rocky Mountain Front-Southern High Plains-
Including the cities of East Glacier Park, Kiowa, Babb,
Saint Mary, Marias Pass, Logan Pass, Browning, Heart Butte,
Dupuyer, Cut Bank, Ethridge, Santa Rita, Rogers Pass, Bynum,
Choteau, and Pendroy
1204 PM MDT Sat Jul 1 2023

...Strong Cross Winds...

Today, strong gusty westerly winds occur along the Rocky Mountain
Front. Sustained winds between 20 to 30 mph with gusts as high as
45 to 55 mph are forecast for this afternoon through early this
evening. Travelers, especially on United States Highway 89 between
Choteau and the International Boundary and United States Highway
2 between Cut Bank and Marias Pass, should be prepared for strong
cross winds. High profile vehicles or those pulling trailers
should be especially cautious and know their vehicles limits when
traveling this afternoon. Additionally, those recreating in the
higher terrain of the Bob Marshall Wilderness and Glacier National
Park should be prepared for strong and gusty winds when
navigating across ridgelines or near saddles.

Fogleman

Preliminary Local Storm Report
National Weather Service Great Falls MT
1220 PM MDT Sat Jul 1 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1215 PM     Tstm Wnd Gst     11 W Helena             46.58N 112.25W
07/01/2023  M51 MPH          Lewis and Clark    MT   Trained Spotter

&&

ML

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